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Native vs. Non-native Species: Who Will Win? Background

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All geographic regions are home to certain organisms that evolved as part of the region's ecosystem. As part of the food web, they are in balance with one another through predator-prey relationships and through competition for resources such as food, water, light, and space. They are called the native species of the region.

When an organism is introduced to a region from a different geographic region, it is called a non-native species. Non-native species sometimes fit well into the existing ecosystem, but they often have negative impacts such as reducing the biodiversity of the region, causing economic losses, and wasting and polluting water resources. They sometimes prey heavily on certain native species, and, because the non-natives may not have any natural predators, they can quickly reduce the populations of the natives. Occasionally this is so severe that it can cause local extinction of the native species. Non-natives are harmful economically when they eat or cause disease in agricultural crops. Finally, non-native plants can cause indirect damage to our water resources because they are not adapted to the region and therefore require extra water, fertilizer, and pesticide. This wastes our water resources and pollutes them through runoff of excess nutrients and toxic chemicals.

Non-native species may be introduced by animals: for example, the seed of a non-native plant may be deposited in the waste of a migratory bird. Non-native species may also be introduced by humans. Some are introduced intentionally, such as garden plants collected by plant enthusiasts. People may also unintentionally carry non-native species when travelling. As the amount of global travel and trade has increased, so has the rate of introduction of non-native species. The United States Geological Survey reported that there were at least 6,271 non-native species established in the United States in 1999 (Baskin, see Resources).

Ironically, a popular control method is to bring in another non-native to exterminate the existing non-native. While this can be an effective strategy, often the new non-native species causes new problems. For example, to control the spread of hydrilla, an underwater plant native to Southeast Asia, the grass carp was introduced to the Chesapeake Bay. The grass carp too is native to Southeast Asia and is a natural predator of hydrilla; however, it also eats the underwater plants native to the Bay, causing a new problem. In an attempt to limit the destruction caused by the grass carp, authorities began using only triploid specimens (i.e., grass carp genetically altered to prevent reproduction). The hope was that the carp, with no offspring, would eventually die off in the Bay. This solution may prove to be ineffective, however, because other cases have illustrated that triploid organisms can revert to being diploid and therefore become capable of reproduction.